Atomic layer etching methods and apparatus

ABSTRACT

A method for performing atomic layer etching of a surface of a substrate is provided, including: performing a surface conversion operation by exposing the surface of the substrate to a surface conversion reactant; performing a ligand exchange operation by exposing the surface of the substrate to a ligand containing reactant; performing a desorption operation that effects removal of surface species from the surface of the substrate; performing a purge operation; repeating the surface conversion operation, the ligand exchange operation, the desorption operation, and the purge operation, for a predefined number of cycles.

BACKGROUND 1. Field of the Disclosure

The present embodiments relate to semiconductor wafer processing, andmore particularly, atomic layer etching (ALE) methods and apparatus.

2. Description of the Related Art

At present, the most extensively used etch process in the semiconductorindustry is a dry plasma etch process known as reactive ion etching(RIE). In RIE, a partially ionized plasma discharge provides a mixtureof reactive and nonreactive ions, electrons, reactive neutrals,passivating species, and photons, with the positively charged ions beingaccelerated normal to the substrate/wafer surface using a negativevoltage bias on the substrate to produce an anisotropic etch. Plasmaetching such as RIE is operated in a continuous fashion, with allreactions occurring simultaneously for the duration of the etch process.This can be beneficial in terms of providing fast etch rates, but alsopresents limitations in that process variability can be significant,with issues of wafer non-uniformity and surface composition/roughnessrequiring costly compensation measures.

As the semiconductor industry has moved towards smaller technology nodesin keeping with Moore's law, the industry is now entering the era ofatomic-scale devices for the sub-10 nm technology node. Such deviceswill require atomic-scale fidelity, with acceptable feature sizevariability on the order of individual atoms expected in the comingyears. The inherent process variability of current industry etchprocesses such as RIE renders them ill-suited for next-generationatomic-scale device manufacturing. Therefore, etch processes withatomic-scale control and minimal variability are sought to enable thesub-10 nm technology node.

It is in this context that embodiments of the disclosures arise.

SUMMARY

Embodiments of the present disclosure provide methods, apparatus, andsystems to enable atomic layer etching.

In some implementations, a method for performing atomic layer etching ofa surface of a substrate is provided, including: performing a surfaceconversion operation by exposing the surface of the substrate to asurface conversion reactant; performing a ligand exchange operation byexposing the surface of the substrate to a ligand containing reactant;performing a desorption operation that effects removal of surfacespecies from the surface of the substrate; performing a purge operation;repeating the surface conversion operation, the ligand exchangeoperation, the desorption operation, and the purge operation, for apredefined number of cycles.

In some implementations, performing the desorption operation includesapplying thermal energy to the substrate.

In some implementations, the applying thermal energy to the substrate isperformed after performing the ligand exchange operation.

In some implementations, the applying thermal energy to the substrate isperformed prior to and/or concurrently with the performing the ligandexchange operation.

In some implementations, the applying thermal energy to the substrateincludes heating a pedestal on which the substrate is disposed and/orheating a process chamber in which the method is performed.

In some implementations, the applying thermal energy to the substrateincludes activating a lamp to provide the thermal energy to the surfaceof the substrate.

In some implementations, performing the desorption operation includesexposing the surface of the substrate to a plasma.

In some implementations, the exposing the surface of the substrate to aplasma includes applying a bias voltage to the substrate.

In some implementations, performing the desorption operation includesexposing the surface of the substrate to a photon source to effectphotolytic desorption.

In some implementations, wherein the surface conversion reactant adsorbsor chemisorbs on the surface of the substrate and modifies surfacespecies on the surface of the substrate, wherein the surface conversionoperation is substantially self-limiting; wherein the ligand containingreactant reacts with the modified surface species to formligand-substituted species that are desorbed from the surface of thesubstrate.

In some implementations, a method for performing atomic layer etching ofa surface of a substrate is provided, including: performing a surfaceconversion operation by moving the substrate into a surface conversionzone of a spatial processing tool, the surface conversion zoneconfigured to expose the surface of the substrate to a surfaceconversion reactant; performing a ligand exchange operation by movingthe substrate into a ligand exchange zone of the spatial processingtool, the ligand exchange zone configured to expose the surface of thesubstrate to a ligand containing reactant; performing a desorptionoperation by moving the substrate into a desorption zone of the spatialprocessing tool, the desorption zone configured to effect removal ofsurface species from the surface of the substrate; repeating the surfaceconversion operation, the ligand exchange operation, and the desorptionoperation, for a predefined number of cycles.

In some implementations, performing the desorption operation includesapplying thermal energy to the substrate.

In some implementations, the applying thermal energy to the substrateincludes activating a lamp to provide the thermal energy to the surfaceof the substrate.

In some implementations, performing the desorption operation includesexposing the surface of the substrate to a plasma.

In some implementations, performing the desorption operation includesexposing the surface of the substrate to a photon source to effectphotolytic desorption.

In some implementations, the surface conversion reactant adsorbs orchemisorbs on the surface of the substrate and modifies surface specieson the surface of the substrate, wherein the surface conversionoperation is substantially self-limiting; wherein the ligand containingreactant reacts with the modified surface species to formligand-substituted species that are desorbed from the surface of thesubstrate.

In some implementations, the method further includes: after performingthe surface conversion operation, performing a first purge by moving thesubstrate through a first purge zone of the spatial processing tool;after performing the ligand exchange operation, performing a secondpurge by moving the substrate through a second purge zone of the spatialprocessing tool; after performing the desorption operation, performing athird purge by moving the substrate through a third purge zone of thespatial processing tool; wherein each of the predefined number of cyclesfurther includes the first, second, and third purges.

Other implementations will be apparent upon consideration of the presentdisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1F conceptually illustrate an ALE process sequence, inaccordance with implementations of the disclosure.

FIG. 2A broadly illustrates a method for performing atomic layer etching(ALE) of a substrate surface, in accordance with implementations of thedisclosure.

FIG. 2B conceptually illustrates a spatial wafer processing sequence, inaccordance with implementations of the disclosure.

FIG. 2C conceptually illustrates a linear spatial wafer processing toolfor performing ALE, in accordance with implementations of thedisclosure.

FIG. 2D conceptually illustrates a carousel spatial wafer processingtool for performing ALE, in accordance with implementations of thedisclosure.

FIG. 2E conceptually illustrates a cross-section view of an exampleprocess station within a multi-station tool, in accordance withimplementations of the disclosure.

FIG. 3 illustrates a substrate processing system 100, which may be usedfor performing temporal based ALE processing of a substrate 301, inaccordance with implementations of the disclosure.

FIG. 4 illustrates a top view of a multi-station processing tool,wherein four processing stations are provided, in accordance withimplementations of the disclosure.

FIG. 5 shows a schematic view of an embodiment of a multi-stationprocessing tool 500 with an inbound load lock 502 and an outbound loadlock 504, in accordance with implementations of the disclosure.

FIG. 6A illustrates an example spatial ALE system, in accordance withone embodiment.

FIG. 6B illustrates an example spatial ALE system, in accordance withone embodiment.

FIG. 7 illustrates a method for performing ALE processing of asubstrate/wafer, in accordance with implementations of the disclosure.

FIG. 8 illustrates a method for performing ALE processing of asubstrate, in accordance with implementations of the disclosure.

FIG. 9 illustrates a method for performing ALE using a halide speciesfor surface conversion, in accordance with implementations of thedisclosure.

FIG. 10 illustrates a method for performing ALE, including a plasmainduced desorption operation, in accordance with implementations of thedisclosure.

FIG. 11 illustrates a method for performing ALE, including a photoninduced desorption operation, in accordance with implementations of thedisclosure.

FIGS. 12A-12F conceptually illustrate an ALE process using targeteddesorption techniques to achieve selective etching on a substrate, inaccordance with implementations of the disclosure.

FIG. 13 illustrates a method for performing ALE of a substrate in aspatial ALE system, in accordance with implementations of thedisclosure.

FIG. 14 illustrates a method for performing ALE processing with in situspectroscopic analysis, in accordance with implementations of thedisclosure.

FIG. 15 illustrates a method for measuring etch of a substrate usingweight, in accordance with implementations of the disclosure.

FIG. 16 illustrates a method for performing ALE of a substrate using amulti-station tool, in accordance with implementations of thedisclosure.

FIG. 17 illustrates a method for performing an ALE process, includingusing a dual pump abatement system, in accordance with implementationsof the disclosure.

FIG. 18 illustrates anisotropic and isotropic etch being promoted viathe application or de-application of bias power, in accordance withimplementations of the disclosure.

FIG. 19A illustrates a system having the aforementioned localizedmulti-gas delivery system 1900, in accordance with implementations ofthe disclosure.

FIG. 19B conceptually illustrates a gas delivery system for deliveringvapor reactants to a process chamber, in accordance with implementationsof the disclosure.

FIG. 20 shows a control module 2000 for controlling the systems of thepresent disclosure.

DESCRIPTION

Embodiments of the disclosure provide methods, apparatus, and systemsfor enabling atomic layer etching. It should be appreciated that thepresent embodiments can be implemented in numerous ways, such as aprocess, an apparatus, a system, a device, or a method. Severalembodiments are described below.

Atomic later etching (ALE) is a technique that removes individualatomic-scale layers of material using a repeated sequence ofself-limiting reactions. Because the reactions in an ALE process areself-limiting, the amount of etching is inherently more controllablewith greater uniformity and consistency as compared to other etchtechniques.

FIGS. 1A-1F conceptually illustrate an ALE process sequence, inaccordance with implementations of the disclosure.

Shown at FIG. 1A is a portion of a surface 100 of a substrate in anunmodified state. The outermost layer 102 of molecules/atoms of thesubstrate surface 100 are exposed for the ALE process. As shown at FIG.1B, a surface conversion/modification operation is performed to convertthe surface layer of the substrate to a functionalized state. Forexample, the surface layer is modified by exposure to a surfaceconversion reactant 104, which may adsorb or chemisorb on the surface.The surface conversion reactant can include molecules or low energyradicals in various implementations, which react with the surface layeratoms to effect the surface conversion step. The resulting surface layeris shown at FIG. 1C consisting of a functionalized outermost layer 106of molecules to enable subsequent ALE steps. As the reaction isself-limiting, only (or substantially only) the outermost layer of thesubstrate surface will undergo conversion. In some implementations, thissurface modification entails conversion of the surface species to ahalide. In some implementations, following the self-limiting surfaceconversion, the chamber is purged to remove any reaction byproducts orexcess surface conversion reactant.

Following the surface conversion operation, then as illustrated at FIG.1D, a ligand exchange reaction/operation is performed. In theillustrated implementation, the modified surface 106 of the substrate isexposed to a ligand containing reactant 108, which effects a ligandexchange reaction wherein the ligand containing reactant adsorbs on thesubstrate surface and transfers its ligands to the converted surfacespecies 106 which were formed during the earlier surfacemodification/conversion operation. The ligands bond with the modifiedsurface layer of molecules/atoms, forming a reaction product consistingof ligand substituted surface species 110 shown at FIG. 1E, which can bereleased as an individual molecule or as a larger combined molecule withthe incoming molecule (dimer, trimer, or even larger clusters).

As shown at FIG. 1F, a desorption operation is performed to effectremoval of the outermost layer of surface species 110 (the reactionproduct following the ligand exchange operation) from the substratesurface. In some implementations, the release can be achieved by theapplication of thermal energy, which can be applied simultaneous withthe exposure to the ligand containing reactant or in a separate step. Insome implementations, the reaction product itself may have a low enoughvapor pressure such that it can be pumped out of the system withoutadditional thermal adjustment. It will be appreciated that the removalprocess should ensure that there is no decomposition of the releasedmolecules, which can be fairly large with multiple attached ligands, toavoid unwanted redeposition back on the wafer.

FIG. 2A broadly illustrates a method for performing atomic layer etching(ALE) of a substrate surface, in accordance with implementations of thedisclosure. At method operation 200, the method initiates withperformance of a surface conversion/modification operation. During thesurface conversion operation, the outermost layer of surfacemolecules/atoms is modified by exposure to a surface conversionreactant, yielding a modified surface layer. The reaction isself-limiting so as to modify only the outermost atomic layer of thesubstrate. At method operation 202, a ligand exchange operation isperformed. During the ligand exchange operation, the substrate isexposed to a ligand-containing reactant, which reacts with the modifiedsurface layer so as to transfer its ligands to the surface layermolecules, e.g. by substituting for ligand species which were formedduring the surface conversion operation.

During the ligand exchange operation, the outermost layer of thesubstrate is transformed into a ligand-containing surface species whichcan be released from the substrate surface in a desorption operation204. In some implementations, the desorption operation 204 occurssimultaneously with the ligand exchange operation, as theligand-containing surface species are released upon their formation.Whereas in other implementations, the desorption operation 204 is aseparate operation performed after completion of the ligand exchangeoperation 202.

Furthermore, in some implementations, instead of a ligand exchangereaction (substitution reaction), a condensation or chelation reactionis utilized to transform the surface species and enable its removal fromthe substrate surface. As noted, the removal can be effectedconcurrently, or via another operation such as by applying thermalenergy to the substrate.

The sequence of the surface conversion operation 200, the ligandexchange operation 202, and the desorption operation 204, define asingle cycle of an atomic layer etch (ALE) process. At method operation206, these ALE operations can be repeated for a predefined number ofcycles, or until a desired etch amount is achieved. For example, in someimplementations, in situ characterization mechanisms (e.g. ellipsometry)can be employed to enable in situ assessment of the etch process anddetermination of when to stop performance of ALE process cycles.

In the case of etching a metallic surface, the surface conversionoperation is generally of the form:

M→MX

where M is a metallic species present at the substrate surface and MX isa converted metallic species, X being representative of a ligand that isintroduced through the surface conversion reaction. For example, wherethe surface metallic species is a metal nitride, the surface conversionoperation may have the following form:

MN→MX+NH3

In another example, where the surface metallic species is a metal oxide,the surface conversion operation may have the following form:

MO→MX+H2O

In some implementations, X is a halide, such as fluorine, chlorine,bromine, or iodine.

Following the surface conversion operation, the ligand exchangeoperation may generally have the following form:

MX (adsorbed)+M′L→ML (adsorbed)+M′X (adsorbed)

where M′L is a ligand containing reactant having a metal M′ and ligandL, ML is a ligand-substituted species (reaction product) after ligandexchange occurs with M′L, and M′X is the reaction byproduct from theligand exchange reaction. The metal M′ is a different metal from themetal M.

The desorption operation generally has the following form:

ML (ads)+M′X (ads)→ML (desorbed)+M′X (desorbed)

As noted above, the resulting molecules may be attached to each otherforming dimers, trimers, or possibly even larger clusters. Examples ofmaterials which may be etched using ALE processes in accordance with thepresent disclosure, include the following: metal oxides, binary metaloxides (M_(x)M′_(y)O_(z)), metal nitrides, binary metal nitrides, metalsulfides, metal phosphides, metal arsenides, metal tellurides, metalsellinides.

When using an acid for the conversion reaction, in the case of an oxide,the reaction will form water; in the case of a nitride, will formammonia; in the case of a sulfide, will form hydrogen sulfide; for aphosphide, will form phosphine (PH₃); for an arsenide, will form arsine;for a telluride, will form tellurium hydride; for a sellinide, will formhydrogen sellinide.

In some implementations, ALE processing is performed at pressures in therange of about 100 mTorr to 10 Torr absolute or partial pressure. Insome implementations, ALE processing is performed at a temperature inthe range of about 100 to 450 C.

In accordance with various implementations, several process flows forperforming ALE are disclosed. In some implementations, an ALE processthat employs fluorine for purposes of surface conversion has reactionsof the following form:

MY_(x) (s)+F source→MF_(z) (s)+Y_(z)H (g),

wherein Y_(x) is an oxide, nitride, metal, or other species, and whereinthe reaction with the F source is a self-limiting thermal, plasma orphotolytic process; and,

MF_(z) (s)+M′L_(n) (g)→ML_(m)F_(z-m) (g)+M′L_(n-m)F_(m) (g),

that is a thermally driven conversion and desorption reaction, and isself-limiting in MF_(z).

An example process for etching aluminum nitride employs the followingreactions:

AlN (s)+3 HF (g)→AlF3 (s)+NH3 (g);

AlF₃ (s)+Al(CH₃)₃ (g)→AlF₂(CH₃) (g)+AlF(CH₃)₂ (g).

An example process for etching aluminum oxide employs the followingreactions:

Al₂O₃ (s)+6 HF (g)→2 AlF₃ (s)+3 H₂O (g);

AlF₃ (s)+Al(CH₃)₃ (g)→AlF₂(CH₃) (g)+AlF(CH₃)₂ (g).

An example process for etching titanium oxide employs the followingreactions:

TiO₂ (s)+4 HF (g)→TiF₄ (s)+2 H₂O (g);

¾TiF₄ (s)+BCl₃ (g)→¾TiCl₄ (g)+BF₃ (g).

It is noted that a plasma process could be used to anisotropically etchafter the thermal conversion step, e.g. using H₂/Ar, BCl₃/Ar or Heplasma.

FIG. 2B conceptually illustrates a spatial wafer processing sequence forperforming ALE, in accordance with implementations of the disclosure. Awafer/substrate can be moved through various process zones of a spatialprocessing tool, with each process zone performing a different functionin the ALE process. It will be appreciated that in some implementations,the wafer is moved to a given process zone in its entirety before theprocess operation of that zone is initiated, whereas in otherimplementations, the process zones are continually active as the wafermoves through them, such that multiple ones of the described operationsmay occur simultaneously across different portions of the waferdepending upon the wafer's positioning within the system. At operation210, the wafer is loaded/input into the tool. At operation 212, thewafer undergoes a first purge operation. At operation 214, the waferundergoes a first conversion reaction (e.g. surface conversionreaction). At operation 216, the wafer undergoes a second purgeoperation. At operation 218, the wafer undergoes a second conversionreaction (e.g. ligand exchange and thermal or other energy application).At operation 220, the wafer undergoes a third purge operation. Atoperation 222, the wafer is output from the process tool.

FIG. 2C conceptually illustrates a linear spatial wafer processing toolfor performing ALE, in accordance with implementations of thedisclosure. A wafer to be processed is loaded to a wafer input stage230. In succession, the wafer is moved through a purge zone 232 thateffects a first purge, a first conversion zone 234 that effects a firstconversion reaction, a purge zone 236 that effects a second purge, asecond conversion zone 238 that effects a second conversion reaction, apurge zone 240 that effects a third purge, and finally to a wafer outputstage 242. The wafer is removed from the wafer output stage 242 afterprocessing is complete.

FIG. 2D conceptually illustrates a carousel spatial wafer processingtool for performing ALE, in accordance with implementations of thedisclosure. A wafer to be processed is loaded to a wafer input/outputstage 251 of a rotating carousel 250. As the carousel 250 is rotated,the wafer is moved to/through various process zones of the tool. Insuccession, the wafer is moved through a purge zone 252 that effects afirst purge, a first conversion zone 254 that effects a first conversionreaction, a purge zone 256 that effects a second purge, a secondconversion zone 258 that effects a second conversion reaction, a purgezone 260 that effects a third purge, and finally back to the waferinput/output stage 251. The wafer is removed from the wafer input/outputstage 251 after processing is complete.

In some implementations, a wafer is moved between a plurality of processstations within a multi-station processing tool. FIG. 2E conceptuallyillustrates a cross-section view of an example process station within amulti-station tool, in accordance with implementations of thedisclosure. Broadly speaking, the process station defines a small volumechamber 272 within a larger chamber 270 with a seal gas 274. The chamber272 is independently exhausted, and enables pressure cycling in a smallvolume for effective dosing/conversion and purging. Such a configurationprovides for isolation of corrosive species, protecting ceramic or metalparts. Also, the configuration provides isolation for contaminationcontrol.

A pedestal 276 supports the wafer during processing. The pedestal may betemperature controlled using a temperature control 278, and bias powercan be controlled using a bias control 280.

The showerhead 282 dispenses process gases into the wafer cavity. Therecan be multiple gas inlets (e.g. dual plenum). The showerhead may haveRF capability (e.g. dual frequency) from an RF source 284, and may betemperature controlled using a temperature control 286.

By way of example without limitation, cleaning can be accomplished usinga remote plasma source or in situ.

The larger chamber 270 may have independent pumping, e.g.

pumping into the chamber 270 through intake 288 and pumping out of thechamber 270 through exhaust 290. Purge capability is provided in thelarger chamber 270 so that when wafers are transferred between stations,they are purged of any process gases or reaction byproducts to avoidcross-contamination between stations. Furthermore, the larger chamber270 is provided with a contamination controlled insert capability toprevent external contamination.

FIG. 3 illustrates a substrate processing system 100, which may be usedfor performing temporal based ALE processing of a substrate 301, inaccordance with implementations of the disclosure. Although FIG. 3 isdescribed in regard to temporal based ALE processing, it should beunderstood that in other implementations, a spatial ALE system canutilize some of the same or similar controls and system facilities,e.g., such as gas feeds, process gases, RF power sources, showerheads,etc.

With this in mind, the system of FIG. 3 includes a chamber 302 having alower chamber portion 302 b and an upper chamber portion 302 a . Acenter column is configured to support a pedestal 340, which in oneembodiment is a powered electrode. The pedestal 340 is electricallycoupled to power supply 304 (e.g., RF power source) via a match network306. The power supply 304 may be defined from a single generator havingtwo or more selectable and mutually exclusive oscillators. The powersupply 304 is controlled by a control module 310, e.g., a controller.The control module 310 is configured to operate the substrate processingsystem 300 by executing process input and control 308. The process inputand control 308 may include process recipes, such as power levels,timing parameters, shuttle speed (for spatial implementations), RF powerlevels, ground settings, process gasses, flow rates, mechanical movementof the substrate 301, etc., such for ALE processing of the substrate301. In spatial ALE implementations, process input may, in someembodiments, provide the timing, speed, duration and motion control of ashuttle to enable spatial ALE processing with a moving RF source.

The center column is also shown to include lift pins 320, which arecontrolled by lift pin control 322. The lift pins 320 are used to raisethe substrate 301 from the pedestal 340 to allow an end-effector to pickthe substrate and to lower the substrate 301 after being placed by theend-effector. The substrate processing system 300 further includes a gassupply manifold 312 that is connected to process gases 314, e.g., gaschemistry supplies from a facility. Depending on the processing beingperformed, the control module 310 controls the delivery of process gases314 via the gas supply manifold 312. The chosen gases are then flowninto the shower head 350 and distributed in a space volume definedbetween the showerhead 350 face which faces the substrate 301 and thesubstrate 301 resting over the pedestal 340. In ALE processes, the gasescan be reactants chosen for surface conversion or for ligand exchangeoperations in accordance with processes described herein.

Further, the gases may be premixed or not. Appropriate valving and massflow control mechanisms may be employed to ensure that the correct gasesare delivered during the deposition and plasma treatment phases of theprocess. Process gases exit the chamber via an outlet. A vacuum pump(e.g., a one or two stage mechanical dry pump and/or a turbomolecularpump) draws process gases out and maintains a suitably low pressurewithin the reactor by a close loop controlled flow restriction device,such as a throttle valve or a pendulum valve.

Also shown is a carrier ring 353 that encircles an outer region of thepedestal 340. The carrier ring 353 is configured to sit over a carrierring support region that is a step down from a substrate support regionin the center of the pedestal 340. The carrier ring includes an outeredge side of its disk structure, e.g., outer radius, and a substrateedge side of its disk structure, e.g., inner radius, that is closest towhere the substrate 301 sits. The substrate edge side of the carrierring includes a plurality of contact support structures which areconfigured to lift the substrate 301 when the carrier ring 353 is liftedby forks 380. The carrier ring 353 is therefore lifted along with thesubstrate 301 and can be rotated to another station, e.g., in amulti-station system, as controlled by carrier ring lift and rotatecontrol 324. In other embodiments, the chamber is a single stationchamber. In still other embodiments, the chamber is part of a spatialALE chamber, which includes a shuttle and an edge ring. The edge ringmay also be referred to as a focus ring, depending on theimplementation.

In some implementations, RF power is supplied to an electrode of thechamber so that a plasma can be generated. In the spatial ALE chamber400, the RF power source is coupled to the shuttle 402, which moves thesubstrate from process zone to process zone to complete one or more filmdeposition steps. More detail regarding a spatial ALE system is providedbelow with reference to FIG. 4.

FIG. 4 illustrates a top view of a multi-station processing tool,wherein four processing stations are provided, in accordance withimplementations of the disclosure. This top view is of the lower chamberbody 302 b (e.g., with the top chamber portion 302 a removed forillustration), wherein four stations are accessed by spider forks 426.Each spider fork or fork includes a first and second arm, each of whichis positioned around a portion of each side of the pedestal 340. In thisview, the spider forks 426 are drawn in dash-lines, to convey that theyare below the carrier ring 400. The spider forks 426, coupled to arotating mechanism 420, are configured to raise up and lift the carrierrings 400 (i.e., from a lower surface of the carrier rings 400) from thestations simultaneously, and then rotate at least one or more stationsbefore lowering the carrier rings 400 (where at least one of the carrierrings supports a wafer 301) to a next location so that furtherprocessing (e.g. etch, deposition, plasma processing, treatment, etc.)can take place on respective wafers 301.

FIG. 5 shows a schematic view of an embodiment of a multi-stationprocessing tool 500 with an inbound load lock 502 and an outbound loadlock 504, in accordance with implementations of the disclosure. A robot506, at atmospheric pressure, is configured to move substrates from acassette loaded through a pod 508 into inbound load lock 502 via anatmospheric port 510. Inbound load lock 502 is coupled to a vacuumsource (not shown) so that, when atmospheric port 510 is closed, inboundload lock 502 may be pumped down. Inbound load lock 502 also includes achamber transport port 516 interfaced with processing chamber 302 b .Thus, when chamber transport 516 is opened, another robot (not shown)may move the substrate from inbound load lock 502 to a pedestal 340 of afirst process station for processing.

The depicted processing chamber 302 b comprises four process stations,numbered from 1 to 4 in the embodiment shown in FIG. 5. In someembodiments, processing chamber 302 b may be configured to maintain alow pressure environment so that substrates may be transferred using acarrier ring 400 among the process stations without experiencing avacuum break and/or air exposure. Each process station depicted in FIG.5 includes a process station substrate holder (shown at 318 for station1) and process gas delivery line inlets.

FIG. 5 also depicts spider forks 426 for transferring substrates withinprocessing chamber 302 b . The spider forks 426 rotate and enabletransfer of wafers from one station to another. The transfer occurs byenabling the spider forks 426 to lift carrier rings 400 from an outerundersurface, which lifts the wafer, and rotates the wafer and carriertogether to the next station. In one configuration, the spider forks 426are made from a ceramic material to withstand high levels of heat duringprocessing.

In some embodiments, a “ring-less” substrate transfer may also beemployed. In such embodiments, the “carrier ring” or “plasma focusingring” remains fixed on one station. The substrate is moved by liftingthe substrate off of the pedestal with pins, inserting a paddle underthe wafer, and then lowering the substrate on pins thus ensuring directcontact with the paddle to substrate. At this point, the substrate isindexed using the paddle to another station. Once the substrate is atthe new station, the substrate is lifted off of the paddle with pins,the paddle is rotated or moved out and the pins are lowered to ensuredirect contact of the substrate to the pedestal. Now, the substrateprocessing can proceed at the new station for the indexed (i.e., moved)substrate. When the system has multiple stations, each of the substrates(i.e., those present at stations) can be transferred together, e.g.,simultaneously, in the similar fashion for ring-less substratetransfers. Additional details regarding multi-station process tools canbe found with reference to U.S. application Ser. No. 14/839,675, filedAug. 28, 2015, entitled “Multi-Station Chamber Having SymmetricGrounding Plate,” the disclosure of which is incorporated by referenceherein.

FIG. 6A illustrates an example spatial ALE system, in accordance withone embodiment. The spatial ALE system 630 includes a plurality ofprocess zones 632, 634, 636, for processing the substrates 640, 642, and646, which are moved through the process zones on a carousel 638.

FIG. 6B illustrates an example spatial ALE system, in accordance withone embodiment. The spatial ALE system includes a chamber 600 that has aplurality of zones for processing the substrate 301. The substrate 301is supported by a shuttle 602, and the shuttle 602 is configured totransport or move the substrate 301 to each of the zones A-D. In oneembodiment, substrates are introduced into the chamber 600 via an accessport 601 a . In some embodiments, an access port 601 b is also providedat the end near zone D. Substrates are introduced into the chamber 600via a load port, which may be interfaced with the access ports. Thechamber 600 is, in one embodiment, under vacuum, so the load portassists in transferring substrates into and out of the chamber 600. Inone embodiment, the chamber 600 may be configured to operate atpressures in the range of about 0.1 to 10 Torr. As shown, a pump 616 mayalso be included as part of the chamber 600, which may assist inremoving gas flows, pumping the chamber to desired pressures, or toenable service operations.

In other embodiments, chamber 600 may be clustered with other chambersor tools, to define a larger architecture system. In some embodiments,fewer zones are provided, such as only providing zones A-C. In general,zone A is configured to provide a reactant gas 608 a , and distributethe reactant gas 608 a over the zone A, such that the reactant gas 608 ais quickly distributed over and reacts with a surface or layer disposedon the substrate 601. In some embodiments, zone B is not required, and asystem may omit processing or structures associated with zone B. In suchcases, the process my progress from zone A (application of reactant A)to zone C (application of reactant C).

A showerhead 620 a is provided in zone A, and is used to provide anddistribute the reactant gas 608 a . In operation, the shuttle 602 willmove the substrate 301 to a location that is under the showerhead 608 aof zone A. Once the gases have been absorbed from reactant gases 608 a ,the shuttle moves the substrate 301 toward zone B. Between zone A andzone B, an isolation surface 626 b is provided. Opposite isolationsurface 626 b is isolation surface 626a. Between the isolation surfaces,which represent lowered structural surfaces or body of the upper chamber600, the zone A is defined. Each of the other zones B, C and D arerespectively disposed between isolation surfaces 626. Isolation surfaces626 b , for example, also include a plurality of inlet ports and outletports. The inlet ports are configured to provide an inert gas and theoutlet ports are configured to remove the inert gas and other gasbyproducts, such as to provide an isolation between the zones.

In the illustrated embodiment, the shuttle will pass under isolationsurface 626 b on its way to zone B, wherein a purge 609 a process isperformed by a purge head 624 a and other gas pumping equipment near oraround zone B. The purge process is configured to evacuate reactantsthat may be disposed over or around the zone B or over the substratewhen present in zone B, i.e., when moved to zone B by the shuttle 602.In one example, the operation in zone B may take between 20 and 300 ms,depending on the recipe being processed. Next, the shuttle 602 is movedto zone C, while passing under isolation surface 626 b . As noted above,isolation surface 626 b is controlled by isolation gas and the inputports and outlet ports that are in communication with isolation gas 610b . Isolation gas 610 a -610 c , for example, are configured to provideinert gas to the input ports of the isolation surface 626 b , and removeinert gas and byproducts of the reacting gases, which may be disposed orrouted to other exhaust infrastructure.

Once the shuttle 602 is moved to zone C, the system controller 610 canbe configured to activate the RF power source 640 that delivers power tothe RF electrodes embedded in the shuttle 602. In some implementations,the electrodes embedded in the shuttle include an RF power electrode andan RF ground electrode. In this manner, the controller 610 can activatethe power source to deliver RF power to the electrodes of the shuttle602 when the shuttle has reached zone C of the chamber 600. In oneembodiment, the RF power provided by the electrodes of the shuttle 602can range between 75 watts and 1000 watts, and in another embodimentbetween 250 watts and 300 watts. The power setting provided duringoperation, which may fall between the above noted ranges, will dependupon the process recipe being implemented in the spatial ALE system.Further, processing in zone C may range between about 25 ms to about 3seconds, on average, depending on the recipe. Again, this duration isbased on the target process, the material types, the etch amount desiredfrom the ALE step, and other variables.

In accordance with some implementations, in zone C, the RF powerprovided to the shuttle 602, having the substrate 301 disposed thereon,will produce a plasma over the surface of the substrate 301. The spacein and around zone C is filled with gas from reactant 608 b , which willbe activated over the surface of the substrate 301 when the power is setto be activated. In one embodiment, the power is set to be activated ina synchronous manner, such that when the substrate 301 reaches an areaunder zone C, the RF power is activated. In one embodiment, the reactant608 b is chosen such that a reaction will occur between the reactant 608b delivered by a showerhead 620 b and the reactant 608 a that wasabsorbed by the substrate in zone A. In one configuration, the shuttle602 has been moved to zone D, where a purge 609 b process is performed,similar to the operation performed in zone B. In zone D, the operationmay last, depending on the desired recipe, between about20 and 150 ms,and in some cases, between about zero and 300 ms.

Additional details regarding spatial processing systems can be found inU.S. application Ser. No. 14/846,697, filed Sep. 4, 2015, entitled“Plasma Excitation for Spatial Atomic Layer Deposition (ALD) Reactors,”the disclosure of which is incorporated by reference herein. Though thedisclosed embodiments of U.S. application Ser. No. 14/846,697 aredescribed with reference to ALD processes, its disclosure can also beapplied for ALE processing, which will be readily apparent to thoseskilled in the art.

FIG. 7 illustrates a method for performing ALE processing of asubstrate/wafer, in accordance with implementations of the disclosure.At method operation 700, the substrate is exposed to a surfaceconversion reactant, which is configured to react in a self-limitingfashion with the outermost layer of surface molecules/atoms on thesubstrate surface. When performed in a temporal ALE system, the surfaceconversion reactant is flowed into the process chamber in which thesubstrate is disposed. Whereas when performed in a spatial ALE system,the substrate is moved into a process region that dispenses the surfaceconversion reactant. The surface conversion reactant reacts with thesurface molecules/atoms to form a converted species.

At method operation 702, a purge operation is performed, to remove anyreaction byproducts and/or any unreacted surface conversion reactant. Ina temporal ALE system, this may be accomplished by purging the chamberwith an inert gas. In a spatial ALE system, the substrate is moved intoa purge region of the ALE system.

At method operation 704, the substrate is exposed to a ligand-containingreactant. In a temporal ALE system, the surface conversion reactant isflowed into the process chamber in which the substrate is disposed.Whereas in a spatial ALE system, the substrate is moved into a processregion that dispenses the surface conversion reactant. Theligand-containing reactant is configured to react with the convertedspecies on the substrate surface in a self-limiting fashion to transformthe converted species into ligand-substituted species on the substratesurface. That is, ligand-containing reactant adsorbs on the substratesurface and the ligands from the ligand-containing reactant aretransferred to the converted species, via a substitution reaction.

At method operation 706, a second purge operation is performed, e.g. byflowing an inert gas into the chamber in a temporal system, or by movingthe substrate into a purge region in a spatial system.

In some implementations, the ligand-substitution reaction also liberatesthe ligand-substituted species from the substrate surface in the samereaction operation. For example, the temperature of the chamber and/orsubstrate may be such that upon formation of the ligand-substitutedspecies, the ligand-substituted species is volatilized and released fromthe substrate surface.

However, in other implementations, the ligand exchange reaction does notalso produce desorption of the ligand-substituted species that is thereaction product, and a separate operation is required to achievedesorption. In accordance with such implementations, with continuedreference to FIG. 7, at method operation 708, thermal energy is appliedto the substrate surface following the purge operation 706, in order toeffect desorption of the ligand-substituted species on the substratesurface. The thermal energy can be applied using any of a variety oftechniques, alone or in combination, in accordance with implementationsof the disclosure. In some implementations, the process chamber isheated in order to provide thermal energy to the substrate, such as byheating the chamber walls and/or heating the pedestal. In someimplementations, the process chamber and/or the substrate are heated byone or more lamps (e.g. infrared lamps). One example of a system usinglamps to transfer energy to a substrate is the SOLA® thermal processingsystem manufactured by Lam Research Corporation.

In some implementations, lasers are used to heat the substrate surface.In some implementations the lasers can be targeted so as to selectivelyheat certain portions of the substrate. The targeted portions will havesufficient thermal energy to achieve desorption of the outer layer ofligand-substituted species, while those portions that are not targetedwill not be etched as they lack the requisite thermal energy to achievedesorption.

In some implementations, the pedestal on which the substrate is situatedis heated so as to transfer heat to the substrate to effect desorption.

At method operation 710, a purge operation is performed to ensurecomplete removal of desorbed species and any other byproducts from theprocess chamber.

In the method of FIG. 7, it will be appreciated that the temperature atwhich the desorption operation is performed is greater than thetemperature at which the ligand exchange operation is performed. In someimplementations, the temperatures at which the surface conversion andthe ligand exchange operations are performed at the same. In otherimplementations, the temperature at which the surface conversionoperation is performed is less than the temperature at which the ligandexchange operation is performed, thus yielding an ALE cycle whereintemperature is progressively increased with each operation of the ALEcycle.

In other words, the surface conversion operation may be performed at afirst temperature, the ligand exchange reaction may be performed at asecond temperature higher than the first temperature, and the desorptionoperation may be performed at a third temperature higher than the secondtemperature. In such implementations, the desorption is performed as aseparate operation from the ligand exchange operation.

It will be appreciated that the reactions/operations which occur duringthe ALE process may be thermally driven, such that the reaction oroperation may not occur unless a threshold temperature is provided as aprocess condition. Therefore, the temperature of the substrate and/orthe process chamber can be controlled so as to provide the appropriatetemperature condition to drive the reactions of the ALE cycle.

In other implementations, the surface conversion is performed at a firsttemperature, and the ligand exchange and desorption are performed in thesame operation at a second temperature higher than the firsttemperature. In such implementations, the ligand exchange reaction anddesorption occur simultaneously or as part of the same operation, as theligand-substituted species are desorbed upon formation.

FIG. 8 illustrates a method for performing ALE processing of asubstrate, in accordance with implementations of the disclosure. Atmethod operation 800, the substrate surface is exposed to a surfaceconversion reactant. At method operation 802, a purge operation isperformed.

At method operation 804, thermal energy is applied to the substratesurface, e.g. by heating the process chamber, the pedestal, and/or thesubstrate directly. Any of the techniques for applying thermal energydescribed above can be employed. The effect is to increase thetemperature of the substrate from the first temperature at which thesurface conversion operation was performed to a higher secondtemperature at which the ligand exchange reaction is performed and atwhich desorption is achieved.

At method operation 806, the substrate surface is exposed to aligand-containing reactant, which adsorbs on the substrate surface toeffect the ligand exchange reaction and desorption of the reactionproduct in the same operation. That is, upon formation of theligand-substituted species (that is the reaction product) through theligand exchange reaction, the ligand-substituted species is configuredto desorb from the substrate surface at the temperature to which thesubstrate and/or the chamber has been heated.

It is noted that for thermal processes such as have been described inthe methods of FIGS. 7 and 8, the etch behavior will typically beisotropic. This is significant as there are not many effective methodsfor achieving isotropic etching, and ALE in accordance withimplementations of the present disclosure can provide isotropic etchingwith atomic scale precision.

FIG. 9 illustrates a method for performing ALE using a halide speciesfor surface conversion, in accordance with implementations of thedisclosure. At method operation 900, a metallic species on a substratesurface is converted to a metal halide by exposure to a halidecontaining reactant.

Examples of metal halides include metal chlorides, metal fluorides,metal bromides, and metal iodides.

Examples of chloride sources include the following: HC1, complexes ofHC1, solutions of HC1, and plasma sources of Cl.

Examples of fluoride sources include the following: anhydrous HF (e.g.employing a low pressure process), adducts of HF (e.g. HF-pyridine)(e.g. employing a low pressure process), solutions of HF (e.g. may usespin-on technique to dispense onto substrate), plasma sources of F (e.g.HF—NF3 plasma) (plasma can be generated in situ or remotely), and otherF sources (e.g. ClF₃, SF₆).

Examples of bromide sources include the following: HBr, complexes ofHBr, solutions of HBr, and plasma sources of Br.

Examples of iodide sources include the following: HI, complexes of HI,solutions of HI, and plasma sources of I.

At method operation 902, a ligand exchange reaction is performed whereinligands of a ligand-containing reactant are substituted for the halidesof the converted surface species on the substrate.

Example of ligand-containing reactants include the following: Sn(acac)2,Al(CH₃)₃, SiCl₄, Al(CH₃)2Cl, TiCl₄, Al(OR)₃, AlCl₃, M(OR)_(n),M(NR₂)_(n), M(acac)_(n), BCl₃.

If necessary, at method operation 904, a desorption operation isperformed to achieve desorption of the reaction product from thesubstrate surface following the ligand exchange reaction. As notedabove, in some implementations, desorption is achieved through theapplication of thermal energy. However, in other implementations, othertechniques can be applied to achieve desorption.

It will be appreciated that the thermodynamics of specific reactions maygovern which reactants are suitable for use in performing ALE onparticular substrate surface species. For example, it is possible toetch alumina with HF and TMA. However, it is not thermodynamicallyfavorable to etch Zirconia with HF and TMA, because while the surfaceconversion can happen, the ligand exchange is thermodynamically uphill.

For an HF conversion for alumina, followed by exposure to silicontetrachloride, up until about 200 C little to no reaction occurs becauseuntil that temperature, the conversion and desorption isthermodynamically uphill. Therefore, it is necessary to provide thermalenergy in order to overcome the kinetic barrier with temperature. Thus,in thermal processes in accordance with implementations of thedisclosure, it is possible to use photo or plasma driven desorption,thereby providing another energy source to induce species desorption.

FIG. 10 illustrates a method for performing ALE, including a plasmainduced desorption operation, in accordance with implementations of thedisclosure. At method operation 1000, a surface conversion operation isperformed on the substrate, as described above in accordance withimplementations of the disclosure. At method operation 1002, a ligandexchange operation is performed on the substrate, also as describedabove in accordance with implementations of the disclosure. At methodoperation 1004, the substrate is exposed to a plasma to effectdesorption and removal of the reaction product and any other byproductsof the ligand exchange operation from substrate surface.

In some implementations, the plasma is generated in situ, for exampleusing an inductively coupled plasma (ICP) mechanism, a capacitivelycoupled plasma (CCP) mechanism, or using microwaves. In otherimplementations, the plasma is generated remotely and supplied to thesubstrate surface.

The plasma activated desorption can occur via various mechanisms. Forexample, the plasma can generate photons (e.g. UV photons), and mayeffect photolytic desorption. The plasma may also generate activatedspecies, such as radicals and/or ions, which promote the desorption. Itwill be appreciated that that the use of plasma-generated radicals willtend to provide isotropic etching.

In some implementations, ion based desorption may tend to beanisotropic. In some implementations, a bias voltage is applied toincrease the anisotropy.

Broadly speaking, when desorption is effected through plasma generatedions, it is desirable to promote a gentle process (as compared to, e.g.,RIE) to avoid sputtering the substrate surface material. Very low energy(e.g. a bias voltage of less than about 50 volts) should be employed toavoid physical etching/sputtering (wherein ion physically knocks offsurface atoms). In ALE, it is desirable to only desorb a singlemonolayer in a given desorption operation. Thus, when using plasma fordesorption, the system can be configured to generate very low ionenergies that only effect desorption without physical sputtering, e.g.with very low bias power.

FIG. 11 illustrates a method for performing ALE, including a photoninduced desorption operation, in accordance with implementations of thedisclosure. At method operation 1100, a surface conversion operation isperformed on the substrate, as described above in accordance withimplementations of the disclosure. At method operation 1102, a ligandexchange operation is performed on the substrate, also as describedabove in accordance with implementations of the disclosure. At methodoperation 1104, the substrate is exposed to photons from a photon sourceto effect desorption and removal of the reaction product and any otherbyproducts of the ligand exchange operation from substrate surface.

The photon activated desorption (photodesorption) can be photolytic innature, wherein the photon breaks bonds of the surface species toachieve cleavage/disassociation from the substrate surface and so enabletheir desorption. In some implementations, the photon exposure produceslocal heating which promotes desorption. It will be appreciated thatthese mechanisms may provide their effects in tandem with one another toachieve photodesorption. In some implementations, the photolytic actionwill cleave the bond to the substrate surface and the local heating willserve to increase volatility of the cleaved species and promote itsremoval.

FIGS. 12A-12F conceptually illustrate an ALE process using targeteddesorption techniques to achieve selective etching on a substrate, inaccordance with implementations of the disclosure. FIG. 12A illustratesa portion of a substrate surface 100, wherein the topmost layer hasundergone a surface conversion reaction to form surface convertedspecies 106. FIG. 12B illustrates the substrate surface following theligand exchange reaction, yielding ligand-substituted species 110 at thesubstrate surface. Targeted thermal or photon energy is applied to thesubstrate surface, which directs the thermal or photon energy tospecific localized region(s) of the substrate surface. Following thislocal application of thermal or photon energy, as shown at FIG. 12C, theligand-substituted species are desorbed and removed from the surface,but only in the region 1200 of the substrate surface, which is a regionat which the thermal/photon energy was directed. The other regions 1202which did not receive the targeted thermal/photon energy did not desorbthe ligand-substituted species. The result is that the region 1200 hasbeen selectively etched.

At FIG. 12D, the next ALE cycle begins with exposure of the substratesurface to the surface conversion reactant, which reacts with theavailable surface species in the region 1200. The otherligand-substituted species which did not desorb in the regions 1202remain on the surface and do not react with the surface conversionreactant. Then at FIG. 12E, the surface converted species in the region1200 undergo the ligand exchange reaction to form ligand-substitutedspecies in the region 1200, and again receives the targetedthermal/photon energy. The targeted thermal/photon energy further movesthe ligand-substituted species in the region 1200, while not removingspecies in the region 1202, yield further selective etching of theregion 1200, as shown at FIG. 12F.

Thus, through the application of targeted thermal or photon energy, aselective etch can be achieved using the ALE techniques of the presentdisclosure. It will be appreciated that in various implementations, thethermal/photon energy can be specifically directed using techniquesknown in the art. For example, techniques for directing photon energyused in the field of photolithography (e.g. lamp/laser light source,projected directly (maskless) or through a photomask) can be applied todirect photon energy to specific locations for desorption in the ALEprocess. It will be appreciated that the locations to which thethermal/photon energy is directed define a pattern for selective etchingvia ALE.

As noted above, ALE can be performed in both temporal and spatialsystems. For temporal processes, the individual reactions are separatedby time, requiring the use of effective purging between reactions, whichis similar to temporal ALD. In a typical temporal process, the wafer isstationary at a station, and the operations are separated by time (bypurges).

However, in spatial processes, the reactions are separated by space. Forexample, a reaction A is performed at location A, which is adjacent to agas/vacuum curtain, which is adjacent to a location B at which areaction B is performed, which is in turn adjacent to another gas/vacuumcurtain. Spatial ALE can be performed using a carousel or linear trackarchitecture. Thus, all reactions are occurring simultaneously atdifferent locations. In a linear tool the process zones are always on,and the wafer is moved into and out of those zones. This is as opposedto multi-station sequential architecture, where wafers are stationaryand run independent processes at each of the stations, and then thewafers are rotated from station to station. Such a multi-station systemcan be characterized as temporal in that the operations are separated bytime, yet the process zones are also spatially separated within thesystem.

FIG. 13 illustrates a method for performing ALE of a substrate in aspatial ALE system, in accordance with implementations of thedisclosure. At method operation 1300, a substrate is moved into asurface conversion zone of a spatial ALE tool, in which the substratesurface is exposed to a surface conversion reactant to effect thesurface conversion reaction. At method operation 1302, the substrate ismoved out of the surface conversion zone of the spatial ALE tool,through a purge zone of the spatial ALE tool.

At method operation 1304, the substrate is moved into a ligand exchangezone of the spatial ALE tool, in which the substrate surface is exposedto a ligand-containing reactant to effect the ligand exchange reaction.At method operation 1306, the substrate is moved out of the ligandexchange zone of the spatial ALE tool, through a purge zone of thespatial ALE tool.

At method operation 1308, the substrate is moved into a desorption zoneof the spatial ALE tool, which is configured to effect desorption of thereaction product (ligand-substituted surface species) from the ligandexchange reaction. At method operation 1310, the substrate is moved outof the desorption zone of the spatial ALE tool, into a purge zone of thespatial ALE tool, to ensure complete removal of desorbed species fromthe substrate surface.

An issue in ALE processing is how to optimize dose times and determinewhen the desired amount of etching has been completed. In someimplementations, a dose characterization can be performed. That is, aseries of ALE process cycles are performed, and the amount of materialremoved is measured. Then it is possible to calculate an etch amount percycle and determine etch rate as a function of dose time. In this way,it is possible to optimize dose time for the ALE process, and the numberof cycles for a given etch operation can be tuned to achieve a desiredetch amount.

In some implementations, desorption is monitored by an in situ infraredspectroscopy or effluent spectroscopy. This can be performed usingtechniques similar to those used for performing endpoint detectionduring a clean process. In some implementations, an IR detector is tunedto detect a characteristic stretch of a desorbed reaction product. Thissignal is monitored, and when the signal diminishes to or below apredefined threshold, then desorption is complete. For example, if anALE process entailed desorption of SiF₄, then an IR detector could betuned to detect the SiF stretch and monitor that signal (similar to aplasma clean for a deposition chamber). Thus, provided there is aspectral band capable of being monitored as an indicator, then it ispossible to use in situ detection to determine when etching is complete.

FIG. 14 illustrates a method for performing ALE processing with in situspectroscopic analysis, in accordance with implementations of thedisclosure. At method operation 1400 a surface conversion operation isperformed on the substrate. At method operation 1402, a ligand exchangeoperation is performed on the substrate. At method operation 1404, adesorption operation is performed on the substrate. At method operation1406, in situ spectroscopy analysis is performed. For example, in someimplementations, an emission corresponding to a desorbed species can bemonitored from the desorption operation, to determine when desorption iscomplete. In some implementations, an emission corresponding to aninterface endpoint can be monitored to determine whether the interfaceendpoint has been reached, which may serve as a signal to stop furtherALE processing. At method operation 1408, the ALE operations (1400,1402, 1404, and 1406) are repeated until a desired etch endpoint isreached, or until a predefined number of cycles is reached.

In some implementations, to characterize an ALE process, a quartzcrystal microbalance can be used to measure weight in situ. This enablesdetermination of weight loss of a thin film as a function of dose.Broadly speaking, the technique entails deposition of a thin film on aquartz crystal, which allows measurement of nanograms or femtograms ofloss. By way of example, consider an ALE process on an aluminum oxide(AlOx) film. The formation of AlF and loss of weight associated withSnAc₂ or TMA ligand exchange and desorption from the aluminum fluoridefilm can be measured. These processes are self limiting in that only thesurface of the AlOx is converted to A1F because there is no diffusion ofF into the AlOx, and the ligand exchange only consumes that amount ofAlF that's formed on the surface and volatilizes the Al compound that'sformed with the tin compound that's formed. Thus, the ALE cycle stopswhen the ligand exchange and desorption are complete through selflimiting mechanisms. It is then possible to measure weight change tocharacterize the ALE process and determine its effect, specifically themass/amount of the AlOx that has been etched.

While a quartz crystal microbalance enables extremely precisemeasurement of weight changes to characterize ALE processes, it does notprovide for measurement on a production wafer. Thus, in someimplementations, ALE system hardware can include an integrated scale ormass comparator for purposes of measuring weight loss resulting fromperformance of an ALE process. In some implementations, a scale can beintegrated into a loadlock to enable measurement of the weight of awafer/substrate before and after ALE processing.

FIG. 15 illustrates a method for measuring etch of a substrate usingweight, in accordance with implementations of the disclosure. At methodoperation 1500, a substrate is measured prior to performance of ALEprocessing. At method operation 1502 a surface conversion operation isperformed on the substrate. At method operation 1504, a ligand exchangeoperation is performed on the substrate. At method operation 1506, adesorption operation is performed on the substrate. At method operation1508, the ALE operations (1502, 1504, and 1506) are repeated for apredefined number of cycles.

At method operation 1510, following completion of the ALE processcycles, the post-etch substrate is weighed. At method operation 1512,the weight loss of the substrate (difference between pre-etch andpost-etch substrate weights) is analyzed. For example, it may bedetermined whether an intended amount of material has been etched, orwhether more or less than the intended amount of material has beenetched. It will be appreciated that the measurement capability of theintegrated scale may not enable monolayer resolution, and therefore, aseries of ALE cycles is performed (for example, to remove on the orderof tens of nanometers of film) before a post-etch weight measurement isdetermined.

It will be appreciated that out-of-chamber metrology analysis can beperformed on an etched wafer/substrate, such as weight analysis and/orspectral ellipsometry.

In various implementations, systems of the present disclosure forperforming ALE, such as those described with reference to FIGS. 3-6, caninclude a variety of features.

In some implementations, systems employ a closed or virtual sealed smallvolume chamber that enables rapid pressurization for the conversion stepand the ligand exchange reaction, and rapid purging/pressure cycling.

For fluoride based ALE processes, systems do not require ceramiccomponents as corrosion is generally not a problem. However, forprocesses using I, Br, or Cl, a ceramic system may be required due tothe potential for etching of aluminum hardware.

A quad architecture (e.g. as employed in the Vector® systemsmanufactured by Lam Research Corporation) enables isolation ofindividual stations, simultaneous processing for throughput enhancement,with individual steps at individual stations. Stations can act as foursmall chambers within a larger chamber, with a virtual seal that enablespressurization in the reaction zone itself. This allows forpressurization during conversion step, and also allows rapiddepressurization and purging.

Reagent/precursor delivery can be provided using a standard gas box,(multiple and simultaneous) liquid delivery, and/or (multiple andsimultaneous) solid delivery. Rapid valve switching and rapid plasmaswitching is useful for providing accurate dosing and minimizingtransition time between reaction/purge processes

In some implementations, ultra small volume dual plenum shower heads areemployed to handle multiple reagents and provide ultra-fast purging.

A point of use valve system can provide for isolation and fastswitching. Point of use valve manifolds can be disposed directly on topof the showerhead.

In some implementations, biased susceptors are provided to promoteanisotropic removal.

FIG. 16 illustrates a method for performing ALE of a substrate using amulti-station tool, in accordance with implementations of thedisclosure. At method operation 1600, the different stations of amulti-station ALE tool are prepared, including being heated topredefined temperatures specific to each station. At method operation1602, a substrate is moved to a surface conversion station of themulti-station ALE tool. At method operation 1604, the substrate surfaceis exposed to a surface conversion reactant while positioned at thesurface conversion station.

At method operation 1606, the substrate is moved to a ligand exchangestation of the multi-station ALE tool. At method operation 1608, thesubstrate surface is exposed to a ligand-containing reactant whilepositioned at the ligand exchange station. In some implementations,desorption also occurs simultaneous with the ligand exchange reaction.However, in other implementations, desorption is performed at adifferent station.

Accordingly, at method operation 1610, the substrate is moved to adesorption station of the multi-station ALE tool. At method operation1612, a desorption operation is performed on the substrate whilepositioned at the desorption station.

In some implementations, a dual pumping system is employed to controleffluent pumping for non compatible effluents. Dry bed absorbers can beused to capture more problematic effluents (e.g. non-volatiles inexhaust). A dual pumping manifold can separate pumping of certaineffluents into different pumps and abatement systems, to avoid saltformation in the exhaust lines.

Single or multi-station systems can have hardware and software thatallows switching between different pump abatement units. For example, insome implementations, each station of a multi-station tool has aseparate pumping manifold that comes to a single line. In someimplementations, the single line can then split into two separateeffluent lines, e.g. one for the surface conversion reaction effluentsand one for the ligand exchange reaction effluents. For example, ifdosing ammonia, effluents from the ammonia dosing step can be pumpedthrough a first pump, and if in another step HCl is produced, then HClcan be pumped through a second pump. If both effluents were pumpedthrough a single pumping manifold they would form ammonium chloride saltthat would precipitate and clog the exhaust system. Thus in instanceswhere the conversion and ligand exchange reactants may form salts, it isuseful to have separate pump systems for each reactant, with one pumpingsystem for the conversion operation and one pumping system for theligand exchange operation.

This is useful for avoiding salt formation in instances such as when ahalide and an amine are used for conversion and ligand exchangereactions. As another example, when using a chloride for conversion andTMA for ligand exchange, aluminum chloride can form, which is not veryvolatile and so will form a salt. Thus, in order to prevent saltformation, it is useful to have one pumping system for conversion andone pumping system for the ligand exchange reaction.

FIG. 17 illustrates a method for performing an ALE process, includingusing a dual pump abatement system, in accordance with implementationsof the disclosure. At method operation 1700, a first pump abatement unitis activated, which is configured to pump effluents from the surfaceconversion reaction. At method operation 1702, the surface conversionreaction is performed, exposing the substrate surface to a surfaceconversion reactant. The effluents from the surface conversion processare pumped away through the first pump abatement unit. At methodoperation 1704, a purge operation is performed to ensure completeremoval of reaction species, which are pumped through the first pumpabatement unit.

At method operation 1706, a second pump abatement unit is activated(with the first pump abatement unit being deactivated), which isconfigured to pump effluents from the ligand exchange reaction. Atmethod operation 1708, the ligand exchange reaction is performed,exposing the substrate surface to a ligand-containing reactant. Theeffluents from the ligand exchange process are pumped away through thesecond pump abatement unit. At method operation 1710, a purge operationis performed to completely remove any remaining reaction species fromthe ligand exchange reaction, which are pumped through the second pumpabatement unit, thereby keeping them separate from those of the previoussurface conversion reaction.

Following are example process conditions for ALE of MN in a Vector®platform (manufactured by Lam Research Corporation): (1) surfaceconversion reaction was effected by NF₃ exposure, specifically, RF basedNF₃, Ar, HF=500 W, ˜2 Torr, 350 C, time <5 s; (2) ligand exchange waseffected by exposure to TMA at 350 C, 4 Torr process, 10% TMA in N₂.

Recently, tungsten hexafluoride (WF₆) etching of TiO₂ and Al₂O₃ filmshas been reported. Systems and methods of the present disclosure can beutilized for such processes.

Existing methods of performing ALE with Sn (tin) containing reactantscan include a hydrogen plasma exposure to remove residual tin. However,in some implementations, instead of exposure to hydrogen plasma toremove residual tin, a desorption operation that is more gentle thanplasma is employed, or which includes a limited dosage of plasma.

In some implementations, temperature control methods, which include useof heat lamps, laser heat emitters, and/or micro-mirror arrays, candirect heat to specific regions of the substrate to cause desorption inspecific areas. In some implementations, micro-mirror arrays can be usedto direct heat to specific areas of the wafer. In some embodiments, themicro-mirror array can be used to direct heat to very specific featuregeometries, similar to lithography processes.

Methods for performing ALE include both temporal ALE methods and spatialALE methods.

In some implementations, ALE methods can include applying bias power tothe chuck to promote anisotropic etching and removing bias power topromote isotropic etching. FIG. 18 illustrates anisotropic and isotropicetch being promoted via the application or de-application of bias power,in accordance with implementations of the disclosure. Furthermore, insome implementations, ALE methods can include controlling the bias powerto enable transitioning between the two modes.

In some implementations, mixed compound (metals/organics) processing isdesired where a wafer has different materials on the surface. There is aneed for applying different treatments to achieve full removal. Forexample, this can include etching compound semiconductors, or alloys. Inone example, it is possible to deliver two types of chemistries, toreact with different types of materials. The delivery can be alternateor be simultaneous. In one example, the surface modification operationcan be the same for both compounds, but the ligand-exchange anddesorption operations can be different for each material.

In some implementations, ALE methods include using different pumps tohandle different types of byproducts. This allows the system to removethe byproducts via different exhaust lines. The method can includedetecting when one material is being removed, and then activating afirst pump, and when the second material is being removed (or detectedto be removed), a second pump can be activated. This method enablesproper handling of byproducts.

In some implementations, methods include controlling etch selectivity oftypes of materials on the wafer. If the wafer has different materialsthat need etching, the system can use temperature control to enableselective etching of one material or another.

In some implementations, temperature control can be used to influenceetching in certain wafer regions and influence deposition in otherregions. In one example, the chuck can be controlled by includingdifferent temperature zones, which are addressable to identify where toheat more or less, so as to influence localized etch or deposition.

In various implementations, specific chemistries/processes are selectedfor specific materials to be etched.

In some implementations, systems include an adjustable temperaturecontrolled chuck for influencing etch performance in specific regions ofthe wafer. Metrology systems may be integrated in a chamber to enablereal-time, in situ measurement, and then temperature control. Chambersmay have metrology for detecting the need to heat specific areas basedon etch performance.

In some implementations, ALE systems include integrated metrology systemfor providing closed-loop monitoring of etch performance. The integratedmetrology can be used, e.g., for determining whether the surface filmhas been etched to the desired thickness.

In some implementations, a dual pumping system is provided forevacuating plasma byproducts, depending on what is being etched.

In some implementations, a localized multi-gas delivery system isprovided, which can be integrated in various zones over the wafer. Thisprovides for fine control over different zones of the wafer, low power,fast switching, enables small chamber gap, without the need for aninductive plasma source. FIG. 19A illustrates a system having theaforementioned localized multi-gas delivery system 1900, in accordancewith implementations of the disclosure.

In various implementations, ALE systems may use a single chamber, ormulti-chamber systems. In multi-chamber systems, different processes canbe carried out in different chambers.

In some implementations, a CCP chamber having the upper electrodeconnected to RF power is employed, and the chuck is held floating. InALE processes, this configuration provides for reduced gaps close to 0.5cm, and also provides for small plasma sheaths.

In some implementations, systems for integrating special liquid deliverysystems to the chamber are provided. FIG. 19B conceptually illustrates agas/vapor delivery system for delivering vapor reactants to a processchamber, in accordance with implementations of the disclosure. In someimplementations, the process chamber 1914 can be a process chamber suchas that of the Kiyo® CX, manufactured by Lam Research Corporation.Broadly speaking, the provided gas/vapor delivery system is capable ofdelivering gas/vapor through injector nozzles 1912 into the processchamber 1914. A gas inlet enclosure 1910 includes gas/vapor lines andcontrollable valves to enable various flows of gas/vapor through thesystem. Gas/vapor that is routed through the gas inlet enclosure 1910can be routed (by controlling the valves) to the injector nozzles 1912to be injected into the process chamber 194, or to the foreline 1904which is exhausted from the system.

As shown, the gas box 1902 connects to the gas inlet enclosure 1910, andalso to the foreline 1904. The gas box 1902 can be configured to provideprocess gases to the gas inlet enclosure 1910 that are routed to theinjector 1912 and into the process chamber.

A vaporizer box 1906 is configured to vaporize a liquid precursor andprovide it to the gas inlet enclosure 1910. For example, the liquidprecursor may be contained in an ampoule that is heated to promotevaporization. In some implementations, the vaporizer box 1906 can beconfigured to provide the vapor either with or without using a push gas(e.g. Ar). The vapor provided from the vaporizer box can be routed viathe gas inlet enclosure 1910 to the injector 1912 or to the foreline1904. In some implementations, the vaporizer box 1906 is also directlyconnected to the foreline 1904.

A purge supply 1908 provides an inert gas for purging (e.g. N₂) both thegas inlet enclosure 1910 as well as the process chamber 1914.

FIG. 20 shows a control module 2000 for controlling the systemsdescribed above. For instance, the control module 2000 may include aprocessor, memory and one or more interfaces. The control module 2000may be employed to control devices in the system based in part on sensedvalues. For example only, the control module 2000 may control one ormore of valves 2002, filter heaters 2004, pumps 2006, and other devices2008 based on the sensed values and other control parameters. Thecontrol module 2000 receives the sensed values from, for example only,pressure manometers 2010, flow meters 2012, temperature sensors 2014,and/or other sensors 2016. The control module 2000 may also be employedto control process conditions during reactant delivery and plasmaprocessing. The control module 2000 will typically include one or morememory devices and one or more processors.

The control module 2000 may control activities of the reactant deliverysystem and plasma processing apparatus. The control module 2000 executescomputer programs including sets of instructions for controlling processtiming, delivery system temperature, pressure differentials across thefilters, valve positions, mixture of gases, chamber pressure, chambertemperature, wafer temperature, RF power levels, wafer ESC or pedestalposition, and other parameters of a particular process. The controlmodule 2000 may also monitor the pressure differential and automaticallyswitch vapor reactant delivery from one or more paths to one or moreother paths. Other computer programs stored on memory devices associatedwith the control module 2000 may be employed in some embodiments.

Typically there will be a user interface associated with the controlmodule 2000. The user interface may include a display 2018 (e.g. adisplay screen and/or graphical software displays of the apparatusand/or process conditions), and user input devices 2020 such as pointingdevices, keyboards, touch screens, microphones, etc.

Computer programs for controlling delivery of reactant, plasmaprocessing and other processes in a process sequence can be written inany conventional computer readable programming language: for example,assembly language, C, C++, Pascal, Fortran or others. Compiled objectcode or script is executed by the processor to perform the tasksidentified in the program.

The control module parameters relate to process conditions such as, forexample, filter pressure differentials, process gas composition and flowrates, temperature, pressure, plasma conditions such as RF power levelsand the low frequency RF frequency, cooling gas pressure, and chamberwall temperature.

The system software may be designed or configured in many differentways. For example, various chamber component subroutines or controlobjects may be written to control operation of the chamber componentsnecessary to carry out the inventive deposition processes. Examples ofprograms or sections of programs for this purpose include substratepositioning code, process gas control code, pressure control code,heater control code, and plasma control code.

A substrate positioning program may include program code for controllingchamber components that are used to load the substrate onto a pedestalor ESC and to control the spacing between the substrate and other partsof the chamber such as a gas inlet and/or target. A process gas controlprogram may include code for controlling gas composition and flow ratesand optionally for flowing gas into the chamber prior to deposition inorder to stabilize the pressure in the chamber. A filter monitoringprogram includes code comparing the measured differential(s) topredetermined value(s) and/or code for switching paths. A pressurecontrol program may include code for controlling the pressure in thechamber by regulating, e.g., a throttle valve in the exhaust system ofthe chamber. A heater control program may include code for controllingthe current to heating units for heating components in the reactantdelivery system, the substrate and/or other portions of the system.Alternatively, the heater control program may control delivery of a heattransfer gas such as helium to the wafer ESC.

Examples of sensors that may be monitored during processing include, butare not limited to, mass flow control modules, pressure sensors such asthe pressure manometers 2010, and thermocouples located in deliverysystem, the pedestal or ESC (e.g. the temperature sensors 2014).Appropriately programmed feedback and control algorithms may be usedwith data from these sensors to maintain desired process conditions. Theforegoing describes implementation of embodiments of the disclosure in asingle or multi-chamber semiconductor processing tool.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, it will be apparent thatcertain changes and modifications can be practiced within the scope ofthe appended claims. Accordingly, the present embodiments are to beconsidered as illustrative and not restrictive, and the embodiments arenot to be limited to the details given herein, but may be modifiedwithin their scope and equivalents of the claims.

What is claimed is:
 1. A method for performing atomic layer etching of asurface of a substrate, comprising: performing a surface conversionoperation by exposing the surface of the substrate to a surfaceconversion reactant; performing a ligand exchange operation by exposingthe surface of the substrate to a ligand containing reactant; performinga desorption operation that effects removal of surface species from thesurface of the substrate; performing a purge operation; repeating thesurface conversion operation, the ligand exchange operation, thedesorption operation, and the purge operation, for a predefined numberof cycles.
 2. The method of claim 1, wherein performing the desorptionoperation includes applying thermal energy to the substrate.
 3. Themethod of claim 2, wherein the applying thermal energy to the substrateis performed after performing the ligand exchange operation.
 4. Themethod of claim 2, wherein the applying thermal energy to the substrateis performed prior to and/or concurrently with the performing the ligandexchange operation.
 5. The method of claim 2, wherein the applyingthermal energy to the substrate includes heating a pedestal on which thesubstrate is disposed and/or heating a process chamber in which themethod is performed.
 6. The method of claim 2, wherein the applyingthermal energy to the substrate includes activating a lamp to providethe thermal energy to the surface of the substrate.
 7. The method ofclaim 1, wherein performing the desorption operation includes exposingthe surface of the substrate to a plasma.
 8. The method of claim 7,wherein the exposing the surface of the substrate to a plasma includesapplying a bias voltage to the substrate.
 9. The method of claim 1,wherein performing the desorption operation includes exposing thesurface of the substrate to a photon source to effect photolyticdesorption.
 10. The method of claim 1, wherein the surface conversionreactant adsorbs or chemisorbs on the surface of the substrate andmodifies surface species on the surface of the substrate, wherein thesurface conversion operation is substantially self-limiting; wherein theligand containing reactant reacts with the modified surface species toform ligand-substituted species that are desorbed from the surface ofthe substrate.
 11. A method for performing atomic layer etching of asurface of a substrate, comprising: performing a surface conversionoperation by moving the substrate into a surface conversion zone of aspatial processing tool, the surface conversion zone configured toexpose the surface of the substrate to a surface conversion reactant;performing a ligand exchange operation by moving the substrate into aligand exchange zone of the spatial processing tool, the ligand exchangezone configured to expose the surface of the substrate to a ligandcontaining reactant; performing a desorption operation by moving thesubstrate into a desorption zone of the spatial processing tool, thedesorption zone configured to effect removal of surface species from thesurface of the substrate; repeating the surface conversion operation,the ligand exchange operation, and the desorption operation, for apredefined number of cycles.
 12. The method of claim 11, whereinperforming the desorption operation includes applying thermal energy tothe substrate.
 13. The method of claim 12, wherein the applying thermalenergy to the substrate includes activating a lamp to provide thethermal energy to the surface of the substrate.
 14. The method of claim12, wherein performing the desorption operation includes exposing thesurface of the substrate to a plasma.
 15. The method of claim 11,wherein performing the desorption operation includes exposing thesurface of the substrate to a photon source to effect photolyticdesorption.
 16. The method of claim 11, wherein the surface conversionreactant adsorbs or chemisorbs on the surface of the substrate andmodifies surface species on the surface of the substrate, wherein thesurface conversion operation is substantially self-limiting; wherein theligand containing reactant reacts with the modified surface species toform ligand-substituted species that are desorbed from the surface ofthe substrate.
 17. The method of claim 11, further comprising: afterperforming the surface conversion operation, performing a first purge bymoving the substrate through a first purge zone of the spatialprocessing tool; after performing the ligand exchange operation,performing a second purge by moving the substrate through a second purgezone of the spatial processing tool; after performing the desorptionoperation, performing a third purge by moving the substrate through athird purge zone of the spatial processing tool; wherein each of thepredefined number of cycles further includes the first, second, andthird purges.